The present invention relates generally to a computer-generated hologram and its fabrication method, and more particularly to a computer-generated hologram capable of reconstructing a full-color image with high resolution, and its fabrication method.
Patent Publication 1 discloses a computer hologram (computer-generated hologram) capable of reconstructing a full-color image under white light and its fabrication method. In the computer hologram set forth in Patent Publication 1,
a recording medium is divided into unit areas;
each unit area is divided into blocks corresponding to red, green and blue sub-areas;
point light sources bearing information about as many RGB colors as the unit areas are provided on the surface of a full-color original image; and
information about colors corresponding to the point light sources bearing information about RGB colors is recorded in the red, green and blue sub-areas in the unit area.
The fabrication method of the prior art is now explained. FIG. 11 is a perspective view of one specific example of the holographic recording method described in Patent Publication 1. In that example, an original image 10 and a recording medium (recording plane) 20 are each horizontally divided by a multiplicity of parallel lines (parallel sections) to define a multiplicity of linear areas. More specifically, as shown in FIG. 11, the original image 10 is divided into a total of 3M unit areas A1, A2, A3, . . . , Am, . . . , AM, and the recording medium 20 is similarly divided into a total of 3M unit areas C1, C2, C3, . . . , Cm, . . . , CM. When the original image is a stereoscopic image, the respective unit areas A1, A2, A3, . . . , Am, . . . , AM are obtained by dividing the surface portion of the solid body. Here, the 3M unit areas on the original image 10 have one-to-one relations to the 3M unit areas on the recording medium 20. For instance, the area Am that is the mth on the original image 10 is corresponding to the mth unit area Cm on the recording medium 20.
And each of the individual unit areas A1, A2, A3, . . . , Am, . . . , AM on the original image 10 becomes a linear area having point light sources lining up in a row. Referring further to FIG. 11, for instance, the mth unit area Am has point light sources Pma1 to PmN lining up in a row. (Although depending on the shape of the object that defines the original image 10, the unit area Am is not always limited to one single line. For instance, if three spheres line up, the section takes on three spherical shapes wherein point light sources line up on the respective circles). As indicated by broken lines in FIG. 12, each unit area C1, C2, C3, . . . , Cm, . . . , CM are divided in three sub-areas. The sub-areas C1r, C2g, C1b here are corresponding to the sub-areas to which the unit area C1 shown in FIG. 11 is divided.
And then, interference fringes about a point of computation Q in any arbitrary unit area on the recording medium 20 are figured out as follows. Although Cmr is here selected as any arbitrary area, it is understood that the same may hold for Cmg and Cmb, too. First, the area Am on the original image 10 that corresponds to the area Cmr to which this point of computation Q belongs is determined as the unit area to be computed. Then, if interference fringes formed at the point of computation Q by synthetic light (object light) including the phase of object light Om1r to OmNr of color R emitted from the point light sources Pm1 to PmN in the unit area Am to be computed (when the area is Cmg or Cmb, there is object light Om1g to OmNg of color G or object light Om1b to OmNb of color B involved) and reference light Lθmr of the same color R are found, it is possible to find interference fringes at the desired point of computation Q. The reference light Lθmr here is a monochromatic parallel light ray parallel with the YZ plane. It is noted, however, that oblique light, not light parallel with the YZ plane, may just as well be used as the reference light Lθmr.
FIG. 13 is a top view illustrative of the conception of such computation processing; it is illustrative of the original image 10 and recording medium 20 of FIG. 11 as viewed from above. As shown in FIG. 13, the necessary object light to find the interference fringes at the point of computation Q is limited to only Om1r, . . . , Omir, . . . , OmNr emitted out of the N point light sources Pm1, Pmi, . . . , PmN in the area Am to be computed about the area Cmr of color R; only Om1g, . . . , Omig, . . . , OmNg emitted out of the N point light sources Pm1, . . . , Pmi, . . . , PmN in the area Am to be computed about the Cmg of color G; and only Om1b, . . . , Omib, . . . , OmNb emitted out of the N point light sources Pm1, . . . , Pmi, . . . , PmN in the area Am to be computed about the area Cmb of color B. In other words, there is no need of factoring in object light from all the point light sources that constitute the original image 10. Thus, if the respective given interference fringes are found about all the points of computation Q defined on the recording medium 20, one is going to obtain the inference fringe distribution on the recording medium 20.
FIG. 14 is a side view of the color original image recorded by such a method as mentioned above, which is under reconstruction. The recording medium 20 is irradiated with white illumination light Lw set in virtual illumination form (parallel light rays parallel with the YZ plane) at an angle α. The areas C1r, C1g, C1b lying at an upper site of the recording medium 20 here are recorded therein with information about the respective color components R, G, B of P1 (a set of P11, . . . , Pli, . . . , P1N is represented by the point light source P1; the same will hold for Pm, PM, too); upon reconstruction, however, reconstructing light for each color component is going to travel in the direction of a virtual point of view E. This will also apply to reconstructing light from the areas Cmr, Cmg, Cmb lying at about the middle of the recording medium 20, and reconstructing light from the areas CMr, CMg, CMb lying at a lower site of the recording medium 20. It follows that if the point of view is placed at the virtual point of view E, reconstructing light for the colors R, G, B about the respective point light sources P1 will be obtained from the areas C1r, C1g, C1b; reconstructing light for the colors R, G, B about the respective point light sources Pm will be obtained from the areas Cmr, Cmg, Cmb; and reconstructing light for the colors R, G, B about the respective point light sources PM will be obtained from the areas CMr, CMg, CMb. Consequently, the color original image 10 constructed of the point light sources P1, . . . , Pm, . . . , PM will be viewed with high color reproducibility.
FIG. 15 is illustrative in schematic of how to fabricate the computer hologram proposed in Patent Publication 1, and what is implicated in FIG. 15 is now explained because it is important for the explanation of the fabrication method according to the invention. As already noted, the original image (object) 10 is divided into a multiplicity of linear unit areas A1, A2, A3, . . . , Am, . . . , AM in the horizontal direction, and the recording medium 20, too, is divided into a multiplicity of linear unit areas C1, C2, C3, . . . , Cm, . . . , CM in the horizontal direction, corresponding to the unit areas A1, A2, A3, . . . , Am, . . . , AM on the original image (object) 10. And, each unit area C1, C2, C3, . . . , Cm, . . . , CM on the recording medium 20 is divided into three sub-areas as indicated by Cmr, Cmg, Cmb as an example. When the width or pitch of the unit areas A1, A2, A3, . . . , Am, . . . , AM on the original image (object) 10 is h, the corresponding width or pitch of the unit areas C1, C2, C3, . . . , Cm, . . . , CM on the recording medium 20 is h. This is implicated by FIG. 15.
Patent Publication 1
    JP (A) 2000-214751Patent Publication 2    JP (A) 2002-72837Patent Publication 3    JP (A) 2005-215570Patent Publication 4    JP (A) 2004-309709Patent Publication 5    JP (A) 2004-309709Non-Patent Publication 1    “99-3D Image Conference '99”, a CD-ROM version of lecturing monographs (at the Shinjuku schoolhouse, Kogakuin University), an article entitled “Image-type binary CGH by means of EB lithography (3)—Enhancement of 3D effect with hidden surface removal and shading—”Non-Patent Publication 2    Junpei Tujiuci, “Holography”, pp. 33-36 (published by Shokabo Publishing Co., Ltd. on Nov. 5, 1997)
If a computer-generated hologram is fabricated by the fabrication method of the aforesaid Patent Publication 1, it is then possible to reconstruct a full-color image with good color reproducibility under white light.
A problem with that method is, however, that in an attempt to record an object having a finer structure on a recording medium, the finer the structure of the object, the finer it is needed to make the unit areas. In other words, once the width of the unit areas provided on the recording medium has been determined, the resolution is limited to that width.